The invention relates generally to control of multiple electrical windfarm systems within an electric power system and more specifically to a master controller and method for controlling a plurality of interconnected windfarms at a point of common coupling with the electric power system.
Typically, an electric power system includes a plurality of power generation assets, which are spread over a geographic area. The electric power system also includes systems that consume power (loads) that may also be spread over the geographic area. The electric power system also includes a grid, a network of electric power lines and associated equipment used to transmit and distribute electricity over a geographic area. The infrastructure of the grid, may include, but is not limited to devices for interconnection, control, maintenance, and improvement of the electric power system operation. Typically, the electric power system includes a centralized control system operatively connected to the power generation assets for controlling a power output of each of the power generation assets, for example, using processing logic. The network operator usually operates the centralized control system. The power output of the power generation assets controlled by the centralized control system may include, but is not limited to an amount of electrical power, and a voltage for the electrical power.
The power generation assets may include individual power generating stations. The power generating station, may for example, each serve a geographic region within the grid by delivering electrical power to such regions. The power generation assets may each include any type of power source. For example, the power generation assets may include a power source that generates electrical power at least partially from coal; hydro; a combustible fluid such as gasoline, natural gas, diesel fuel, etc.; and from nuclear, wind, and solar energy.
Wind energy is often used to generate electrical power at power plants, often referred to as windfarms, using, for example, the rotation of large wind turbines to drive electrical generators. Windfarms and their associated windfarm controllers can control reactive power supply, and to a more limited extent active power. Larsen, in U.S. Pat. Nos. 7,119,456, 7,166,928, and 7,224,081, describes a voltage control for wind generators including a farm-level controller with a reactive power command and a wind turbine generator control system. Wind turbine generator voltage control may be provided by regulating the voltage according to a reference set by a higher-than-generator-level (substation or farm level) controller. Reactive power may be regulated over a longer term (e.g. few seconds) while wind turbine generator terminal voltage is regulated over a shorter term (e.g. fraction of a second) to mitigate the effect of fast grid transients.
For economic reasons and as one of the approaches to reduce the environmental impacts of fossil fuel power generation, wind turbine generators with larger power output are being produced and windfarms with greater numbers of wind turbine generators are being brought into operation. The power output from the windfarms in the future may comprise a significantly larger part of the total power being supplied and transmitted along the transmission grid. Often, an original windfarm may be sited at a certain geographic location, based on desirable wind conditions at that location. Later, one or more additional windfarms may be sited at the same geographic area, based on the desirable wind conditions that motivated the first windfarm. The later windfarms may be built by the same operator as the first windfarm or by completely different operators. The outputs from windfarms may be interconnected in a variety of points, which are ultimately tied together at a point of common coupling. The point of common coupling may also be the point of connection to the electric power system grid. The point of common coupling may provide a location for measurement of combined output parameters from the plurality of interconnected windfarms. Alternatively, the point of common coupling may be remote from the point of interconnection with grid. Often it is desirable to regulate the combined power-related output from multiple windfarms at the location of measurement. However, at other times it may be desirable or necessary to regulate the combined power-related output from multiple windfarms at a point of regulation distant from the location at which the combined parameters may be measured, for example at the point of interconnection with the grid.
FIG. 1 illustrates a plurality of local windfarms 10, 15, 20 (three windfarms are shown, but any number of local windfarms may be tied together) each with a local windfarm controller 60, interconnected with each other at a point of common coupling 25. The point of common coupling 25 may be at the same point of the physical connection 27 an electrical power system grid 30. For each local windfarm 10, 15, 20, one individual wind turbine generator 35 is shown, representing multiple wind turbine generators usually present in a local windfarm. Each individual wind turbine generator 35 of a local windfarm may be connected through an output transformer 40 to a common bus 45 for the local windfarm, and then through a windfarm transformer 50 to interconnecting lines 55 between the plurality of local windfarms. The local windfarm controller 60 may be operatively connected to the individual wind turbine generator 35 to provide commands 61 for control of power-related parameters. The local windfarm controller 60 may also receive operational status signals 62 from the wind turbine generators and sense power-related output parameters 63 at an output measurement point 65 for the local windfarm 10, 15, 20.
The interconnection of the windfarms may be in different configurations. The distances between the windfarms may vary. The number of wind turbine generators in the individual windfarms may be different. Further, the point of physical connection with the grid may be remote from any of the individual windfarms and the point of common coupling.
As previously described, the centralized control system is operatively connected to the power generation assets for controlling power output parameters. In the case of the plurality of interconnected windfarms with individual local windfarm controllers, individual local power-related commands may be provided to the individual local windfarm controllers from the central control system. Typically, the power-related commands provided to the local windfarm controller may direct the local windfarm controller to provide a specific power-related output at the point of common connection. However, the plurality of individual local windfarm controllers cannot control at the point of common coupling 25 because the power-related parameters at that point are a combination of the outputs from all of the individual windfarms. Typically such problems have been side stepped by reducing regulating requirements, or constraining operation.
Consideration has been given to tuning the individual wind farms to be less dynamic in a way that naturally minimizes interactions. This approach may often reduce the regulation quality and may not ultimately meet the requirements for the power system interconnect standards. Every windfarm could also be instrumented to monitor the output from every other windfarms, as well as the point of interconnect, and derive its own contribution required to regulate the point of interconnect quantities. This solution is a more expensive approach, requiring extra measurement instrumentation and control complexity, such that the complexity makes it difficult to apply.
Accordingly, there is a need to provide a structure and method for controlling a plurality of interconnected windfarms, each operating with a local windfarm controller and jointly providing power-related parameters at a point of common connection with the grid of an electric power system.